1. Field of the Invention
The present invention relates to a key for a keyboard instrument, which is pivotally moved in accordance with key depression, and more particularly to a key for an acoustic piano and the like, which uses bushing cloth in engaging portions for engaging between the key and pins.
2. Description of the Related Art
Conventionally, as a key for a keyboard instrument of this kind, one disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H09-258720 is known. This key is for an upright piano, and includes a key stick extending in a front-rear direction. The key stick has a balance rail pin hole formed in the center thereof such that it vertically extends therethrough. The balance rail pin hole has left and right wall surfaces opposed to each other, and sheets of bushing cloth are affixed to the respective left and right wall surfaces. Further, the key stick has a front rail pin hole formed in a front end of a lower surface thereof such that it opens downward. Sheets of bushing cloth are also affixed to respective left and right wall surfaces of the front rail pin hole.
The above bushing cloth is formed by coating woolen cloth with a fluorocarbon resin, and is manufactured as follows: First, cloth formed by weaving wool fibers is immersed in an aqueous solution of a fluorocarbon resin to be impregnated therewith such that the cloth is saturated with the fluorocarbon resin to thereby coat the surfaces of the wool fibers with the fluorocarbon resin. Next, the cloth is taken out of the aqueous solution of the fluorocarbon resin, and is then sequentially dried and heated at a predetermined temperature for a predetermined time period to cure the fluorocarbon resin, whereby the bushing cloth is manufactured.
The key configured as above is pivotally supported by a keyframe in a state in which the balance rail pin hole is engaged with a balance rail pin via the bushing cloth sheets affixed to the left and right wall surfaces of the balance rail pin. Further, the front rail pin hole is engaged with a front rail pin via the bushing cloth sheets affixed to the left and right wall surfaces of the front rail pin hole. When the key is depressed, the key is pivotally moved about the balance rail pin. At this time, the bushing cloth affixed to the balance rail pin hole and the front rail pin hole is brought into sliding contact with the balance rail pin and the front rail pin, respectively. Further, shakes of the key in a left-right direction are prevented by the front rail pin.
However, the conventional bushing cloth is formed simply by coating the surfaces of the wool fibers with the fluorocarbon resin, and hence when the bushing cloth is repeatedly slid along the balance rail pin and the like in accordance with key depressions, the fluorocarbon resin can wear or fall off the surfaces of the wool fibers. In this case, the wool fibers are exposed to be brought into direct contact with e.g. the balance rail pin. In this state, since the abrasion resistance of the wool fibers is lower than that of the fluorocarbon resin, the abrasion of the bushing cloth is advanced to make wobbling of the key liable to occur. Further, since the lubricity of the wool fibers is lower than that of the fluorocarbon resin, noise becomes liable to occur during the pivotal motion of the key, which obstructs the smooth pivotal motions of the key.
Further, as described above, to coat the surfaces of the wool fibers with the fluorocarbon resin, the bushing cloth is required to be manufactured through a large number of steps e.g. of impregnation, drying and heating of the fluorocarbon resin. This causes an increase in the manufacturing costs of the key.